Various types of radiation image capturing devices such as a so-called direct-type radiation image capturing device and a so-called indirect-type radiation image have been developed. The direct-type radiation image capturing device generates electric charge with a detection element in accordance with the dose of radiation such as X-rays, and converts the generated charge into electric signals. The indirect-type radiation image capturing device converts radiation with a scintillator or the like into electromagnetic waves having a different wavelength from the radiation such as visible light, generates charge with a photoelectric conversion element such as a photodiode in accordance with the energy of the converted electromagnetic waves thereafter, and converts the generated charge into electric signals. In the present invention, the detection element in the direct-type radiation image capturing device and the photoelectric conversion element in the indirect-type radiation image capturing device are referred to as radiation detection elements.
Each of these types of radiation image capturing devices is known as an FPD (Flat Panel Detector), and is conventionally formed to be united with a supporting stand (or a Bucky device). (Refer to Patent Document 1, for example.) However, in recent years, a portable radiation image capturing device including a radiation detection element and the like housed in a housing has been developed and in practical use. (Refer to Patent Documents 2 and 3, for example.)
By the way, among these types of radiation image capturing devices, in particular, some portable radiation image capturing device is configured to read image data from radiation detection elements after irradiation is performed, in response to the information on the start and/or the end of the irradiation transmitted from an external device, such as a computer, which manages an irradiation device or a system.
However, to do that, it is necessary to interface a radiation image capturing device with an irradiation device, a computer, or the like, and build a control configuration of a system including the irradiation device, the computer, or the like, as a whole. Hence, the configuration of the radiation image capturing device to recognize the start and/or the end of irradiation becomes on a large-scale. Therefore, it is desired that a radiation image capturing device is configured to be able to detect the start and/or the end of irradiation by itself.
In order to make a radiation image capturing device detect the start and the like of irradiation by itself, the radiation image capturing device may be configured to include a sensor and the like, and detect the start and/or the end of irradiation with the sensor. However, in this case, a space to provide the sensor is needed in the radiation image capturing device, and hence the radiation image capturing device becomes larger. In addition, when a sensor is provided therein, more power is consumed for the sensor to be driven. This is a problem particularly for a portable radiation image capturing device because a built-in battery thereof is consumed.
Hence, as shown in FIG. 7 described below, for example, it is proposed to detect current flowing in bias lines 9 for applying a bias voltage from a bias power supply 14 to radiation detection elements, or detect current flowing in a connection line 10 for the bias lines 9, and, by utilizing the fact that when the radiation detection elements are irradiated, electron-hole pairs are generated in the irradiated radiation detection elements and the current flows in the bias lines 9, detect the start and/or the end of irradiation from the increase and/or the decrease of the current value of the current. (Refer to Patent Document 4, for example.)
As described above, in the case where the current flowing in the bias lines 9 and/or the connection line 10 is detected so that the start and/or the end of the irradiation is detected from the increase and/or the decrease of the current value, the current flowing in the bias lines 9 and/or the connection line 10 accompanying the irradiation easily flows therein when switch sections of TFTs 8 (Thin Film Transistor, shown in FIG. 7 and the like) connected to radiation detection elements are on so that the gates of the TFTs 8 are opened.
Hence, some radiation image capturing device is configured to monitor the current flowing in the bias lines 9 or the like with the TFTs 8 on, and detect the start of the irradiation by detecting the increase of the current. Note that, if, after the start of the irradiation is detected, the TFTs 8 are kept on, charge (image data) generated in the radiation detection elements 7 by irradiation is discharged from the radiation detection elements 7. Hence, in order to switch to a mode in which the charge (image data) is accumulated, the TFTs 8 are turned off.